Preservation of Quaternary sediments in DSGSD environments: the Mont Fallère case study (Aosta Valley, NW Italy)

The DSGSDs recognized in the western Alps, usually affecting a glacial valley, produce a strong deformation both of the bedrock and Quaternary cover, generally favoring the erosion. The current research, that regards the DSGSDs occurring in the M. Fallére southern slope in the Aosta Valley, suggests that these DSGSDs can also locally favor the formation and preservation of the Quaternary stratigraphic record for these following reasons: - development of transversal elongated depressions, essentially connected with the onset of gravitational structures (trenches minor scarps and counterscarps), filled by differentiated Quaternary successions; - occurrence of closed depressions along the slope, essentially due to gradual evolution of gravitational structures (trenches or minor scarps and associated counterscarps), occupied by lakes progressively filled by subglacial, lacustrine and palustrine sequences; - occurrence of wide flat, irregular surfaces, characterized by lower erosional phenomena respect to the surrounding steep slopes and preserving various Quaternary stratigraphic successions; - development of rounded reliefs and associated wide depressions, both with topographic surface hanging over the torrential incisions that are located along the fractures: this morphology favors the preservation of glacial, outwash, lacustrine and palustrine sediments; - wide colluvial and debris cover, that buries and partly preserves the older Quaternary sediments; - local occurrence of a travertine cover and cementation of sediments, that help to preserve the older Quaternary sediments. This described morphological conditions are favorable to prehistoric human settlements, resulting in archaeological mountain sites that also provide a chronological reference for the DSGSD evolution.